The XCreateIC
function creates a context within the specified input method.

Some of
the arguments are mandatory at creation time, and the input context will
not be created if those arguments are not provided. The mandatory arguments
are the input style and the set of text callbacks (if the input style selected
requires callbacks). All other input context values can be set later.

XCreateIC
returns a NULL value if no input context could be created. A NULL value
could be returned for any of the following reasons: